Stars, starlight AND Light Information

OUTCOME QUESTION(S): S1-4-06: S1-4-07: How do astronomers measure the great distances in the universe? S1-4-07: What can an astronomer learn about a star by looking at light? Vocabulary & Concepts  Astronomical Unit Light-year Apparent magnitude Absolute magnitude Electromagnetic Energy Spectroscope

Scientific Notation (x 10X) Express very large or very small numbers “Power of 10” equals the number of places the decimal was moved (+) large, (-) small 32 000 000.0 is 3.2 x 107 0.0000000055 is 5.5 x 10-9 2.6 x 105 is 260 000.0 2.6 x 10-5 is 0.000026 A positive exponent (107) means multiply by 10 that many times A negative exponent (10-5) means divide by 10 that many times

Earth to the Sun: 1 AU = 1.5 x 108 km (150000000) Distance and the Universe Common to use Astronomical Unit (A.U.) 1 A.U. = distance between the Earth and the Sun Common Distances: Sun - Pluto: ~ 40 AU Sun - Saturn: ~ 10 AU Sun - Jupiter: ~ 5 AU Sun - Mars: ~ 1.5 AU So Pluto is 40x farther away from the Sun than Earth Earth to the Sun: 1 AU = 1.5 x 108 km (150000000)

Nearest star - 4.1 x 1013 km away from Earth! That’s 41,000,000,000,000 km! Nearest star - 4.1 x 1013 km away from Earth! This star is Proxima Centari Light-year (LY): The distance a beam of light travels in one year Light moves outward fast – about 300,000 km/sec. 9.46 x 1012 km /year = 1 light-year P. Centari is 4.3 light-years away

Bright stars look close, but may be very far away Distances can be deceiving: Bright stars look close, but may be very far away Star Approx. Distance (LY) P. Centari 4.3 Sirius 8.8 Betelguese 700 Rigel 900 Most distant known galaxy 15,000,000,000 Star light takes years to get to Earth – this delay means we are looking at old “images” – it’s like looking into the past…

Luminosity (brightness) Star light can be used to determine temperature, composition and size (mass) Luminosity (brightness) There are two amounts (magnitudes) of brightness: Apparent magnitude – brightness as we see it. Absolute magnitude – actual brightness. The Sun has a higher apparent magnitude, since it is so much closer than other stars

Star B looks brighter – more apparent magnitude Star B is closer to us than Star A Star B and A have the same absolute magnitude

Despite being cooler, the Sun is still bigger than about 95% of stars Temperature of Colour Colour – shows how much energy a star emits. Colder star glows red Hotter star glows bluish white or even blue Colour Temperature (oC) Example Blue 25,000 – 50, 000 Bluish-white 11,000 – 25,000 Rigel (Orion’s belt) White 7,500 – 11,000 Sirius (brightest) Yellowish-white 6,000 – 7,500 Polaris Yellow 5,000 – 6,000 Sun Orange 3,500 – 5,000 Red 2,000 – 3,500 P. Centauri (closest) Despite being cooler, the Sun is still bigger than about 95% of stars

Notice bigger stars are not necessarily hotter…but usually brighter

Star Composition Light is a type of energy called: Electromagnetic Energy Scientists use a spectroscope to analyse the light energy coming from stars Spectroscope – tool that splits light into a pattern of colours, like a rainbow.

Showing as the “black” lines of missing energy The elements that make the star will absorb unique parts of the spectrum as energy is released. Showing as the “black” lines of missing energy The black lines in the spectrum are used to identify the elements that make up the star.

Remember your chemistry: heated compounds give off a unique colour spectrum. Scientists have heated elements and recorded the unique light energy patterns The “missing” black lines in the spectra of the Sun match with the known spectra of Hydrogen but not with Mercury – so the Sun contains Hydrogen!

CAN YOU ANSWER THESE QUESTIONS? S1-4-06: How do astronomers measure the great distances in the universe? S1-4-07: What can an astronomer learn about a star by looking at light? Vocabulary & Concepts  Astronomical Unit Light-year Apparent magnitude Absolute magnitude Electromagnetic energy Spectroscope